This invention relates to tire building methods and apparatus. More particularly, the invention relates to a two stage tire building system, which is used, for example, in the building of radial tires having more uniform tire cord lengths.
A typical two stage tire building system employs a first stage, cylindrical, tire building drum on which is formed a cylindrical tire carcass from layered unvulcanized components of the tire, such as an inner liner and one or more carcass plies, plus flippers or chippers that may be desired in the area of the tire beads. The cylindrical tire carcass is then removed from the first stage tire building drum and transported to a second stage, expandable tire building drum where the carcass is expanded into a toroidal shape for receipt of the remaining components of the tire, such as sidewalls, the unvulcanized tread and reinforcement belts. The completed, toroidally shaped unvulcanized tire carcass is then removed from the second stage drum and subsequently molded and vulcanized into a finished radial tire.
In a well known two stage system, the tire beads with attached unvulcanized rubber apexes are positioned in spaced, unattached surrounding relation around the unvulcanized, cylindrical tire carcass which was built on a first stage cylindrical tire building drum. The tire carcass is lifted off the first stage solid drum by means of suction cups which grab and hold the carcass. The carcass and the unattached tire beads are then transported axially to the expandable second stage tire shaping drum, which is coaxially aligned with the first stage tire building drum.
On the second stage drum, the opposing ends of the tire carcass are turned up around the tire beads to fix their maximum axial separation distance. Then, the tire carcass is expanded into a toroidal shape; this action also serving to limit the beads"" minimum axial separation distance. A belt and tread structure is applied centrally around the tire carcass having a toroidal shape to complete formation of an unvulcanized tire carcass which is suitable for molding and vulcanization.
In these prior art tire building systems, a problem arises in precisely locating and anchoring the tire beads on the unvulcanized tire carcass, especially during the transportation of the tire beads from the first stage drum to the second stage drum. It is desired to position the beads so that tires can be built without distortion caused by variations in their positioning.
European Patent Application Publication number 0,449,587A1 (Oakafuji/Bridgestone Corp., October 1991) discloses a cylindrical member removal and transfer method that utilizes a band removal unit (18) having holding pawls (20) engaged with the bead rings (14), and frustoconical expanding pawls (22) that expand the ends of the cylindrical member (16). The two sets of pawls are used to maintain the shape of the member and the position of the bead rings during transfer from a first stage drum to a second stage drum.
It is an object of the present invention to provide a two stage tire building system which can be used to build radial tires having more uniform tire cord lengths, as defined in one or more of the appended claims and as such, having the capability of accomplishing one or more of the following subsidiary objects.
An object of the present invention is to provide a method of constructing radial tires having more uniform tire cord lengths.
Still another object of the present invention is provide a tire building method whereby a tire""s sidewalls may be applied while the tire carcass is on a first stage, tire building drum; such a method allowing for an easier and more accurate positioning of the sidewalls.
Other objects and advantages of this invention will become readily apparent as the invention is better understood by reference to the accompanying drawings and the detailed description that follows.
The present invention is a method and system for building, in at least two stages, an unvulcanized tire carcass suitable for molding into a beaded, finished tire having more uniform tire cord lengths, and whereby a tire""s sidewalls may be applied while the tire carcass is on a first stage, tire building drum.
In accordance with one preferred embodiment of the present invention, the system is characterized by: (a) a first stage, expandable drum on which unvulcanized tire building components are layered to form a cylindrically shaped, unvulcanized tire carcass; (b) a second stage, shaping drum on which the tire carcass is shaped into a shape suitable for subsequent molding and vulcanization; and (c) a bead tube transfer device that loads and positions beads on the tire carcass that is built up on the first stage drum and then transfers the tire carcass and its beads between the first and second stage drums while precisely maintaining the axial separation distance between the carcass"" beads.
In this preferred embodiment, on each end of the first stage drum there is attached an inflatable bladder, which upon inflation serves to turn up the adjoining carcass distal end. Additionally, the bead tube transfer device holds the ends of the carcass in a turned up position during the transfer between the first and second stage drums to allow the carcass and its beads to be clamped by shaping drum bead clamp segments such that the beads"" axial separation distance on the second stage, shaping drum is substantially the same as that set on the first stage drum.
In another preferred embodiment, the first stage drum further has on each of its ends a retractable end bell that covers the inflatable bladders while the unvulcanized components are being built up and layered onto the drum. The end bells are mounted so as to allow for axial, retracting motion which serves to fully expose the inflatable bladders so that they may operate to turn up the carcass ends.
Additionally, the second stage drum has inner and outer inflatable bladders that are mounted on outer shaping drum surfaces and proximate the bead clamping segments. When inflated, the inflatable bladders work in conjunction with the bead clamping segments to prevent a tire""s beads from moving and becoming misaligned during the tire building operations of the second stage shaping drum.
Further, the bead tube transfer device has at least two, main support rings configured and oriented to encompass the ends of a tire carcass. These support rings are mounted so that their axial separation distance can be varied. This device also has bead tube flanges mounted on the rings, the bead tube flanges having a perforated outer surface and configured so that a portion of the perforated surface comes into contact with the turned up, distal ends of the carcass. The perforations allow a vacuum to be imposed on a portion of the bead tube flange outer surface so as to aid in maintaining the ends of the carcass in a turned up position.
The bead tube transfer device further has at least two vacuum rings oriented outside of and approximately parallel to the main support rings. These vacuum rings are configured to encompass the ends of a tire carcass. They impose a vacuum on a portion of the carcass turned up ends so as to aid in maintaining the ends of the carcass in a turned up position. Additionally, the bead tube flange outer surfaces have magnets mounted on them for holding the beads next to the flanges.
In another preferred embodiment, the bead tube transfer device further includes a bead centering and loading device for placing beads on a tire carcass.
In another preferred embodiment, the present invention takes the form of a method for building, in at least two stages, an unvulcanized tire carcass and bead assembly suitable for molding into a finished tire. The method comprises the steps of; (a) layering unvulcanized tire building components on a first stage, expandable drum to form a cylindrically shaped, unvulcanized tire carcass; (b) placing a pair of tire beads in parallel relation around the first stage drum in spaced relation from the cylindrical tire carcass thereon, such that the ends of the tire carcass extend laterally beyond the tire beads; (c) expanding radially the first stage drum and the tire carcass thereon into engagement with the tire beads, and at least partially turning up the tire carcass ends around the tire beads to at least partially fix and lock the beads to the tire carcass; (d) transferring with a bead tube transfer device the tire beads and engaged tire carcass having at least partially turned up ends from the first stage drum to a second stage shaping drum having radially extendible, bead clamping segments, the bead tube transfer device having the capability to precisely maintain the bead axial separation distance during the transfer and positioning of the beads and engaged carcass onto the second stage drum; (e) clamping, with the second stage drum""s bead clamping segments, the beads to the carcass so as to precisely maintain on the second stage drum the bead axial spacing initially fixed on the first stage drum; and (f) shaping the carcass on the second stage drum and completing other predetermined second stage operations, such as completion of turning up the tire carcass distal ends so that the tire carcass ends clamp and lock the beads, applying a belt and tread structure to the tire carcass.
The preferred embodiments of the system and method so described are seen to provide the capability for the unvulcanized tire building components for use on the first stage drum to include a pair of sidewalls.